Create .mojo applications in a common subdir under out/Debug

mojo/services/catalog/catalog.cc

Index: mojo/services/catalog/catalog.cc
diff --git a/mojo/services/catalog/catalog.cc b/mojo/services/catalog/catalog.cc
index 35af6b0428d0ee2b44e583bc2f4c938910f01eb2..456bc30009f9a5c4a5301dbccb4f3cd5f91b304f 100644
--- a/mojo/services/catalog/catalog.cc
+++ b/mojo/services/catalog/catalog.cc
@@ -81,6 +81,8 @@ Catalog::Catalog(scoped_ptr<Store> store,
       system_catalog_(system_catalog),
       weak_factory_(this) {
   PathService::Get(base::DIR_MODULE, &system_package_dir_);
+  system_package_dir_ =
+      system_package_dir_.Append(FILE_PATH_LITERAL("Mojo Applications"));
   DeserializeCatalog();
 }